1. Field of the Art
The present invention relates to a novel optically active titanium complex and the ligand thereof, and a production method of optically active epoxy compound by use of the complex.
2. Description of the Related Art
Optically active epoxy compounds have been widely used as intermediates of several medicines represented by optically active benzopyran compounds that are effective for treating hypertension, asthma or the like, and the synthetic methods of the compounds have been widely considered. Among the synthetic methods, asymmetric epoxidation of carbon-carbon double bond is the most practical method, since asymmetric epoxidation by use of titanium tartrate as a catalyst was found (Non-patent document 1), several synthetic methods through asymmetric epoxidation have been developed (Non-patent Documents 2 and 3).
However, many of these synthetic methods are methods in which an oxidizing agent having a low atom economy, such as hypochlorite, iodobenzene or the like is used. Thus, it is strongly desired to develop any methods having a higher atom economy and further any synthetic methods by use of an environment-friendly oxidizing agent. Among several oxidizing agents, hydrogen peroxide is said to be an environment-friendly oxidizing agent as it has a high atom economy and it is transformed into water after oxidation. Therefore, asymmetric epoxidations by use of hydrogen peroxide as an oxidizing agent have been eagerly studied, but only a few examples can achieve epoxidation in a high enantioselectivity manner (Non-patent Documents 4 and 5), and in many cases there is a problem that the turnover number of catalysts is insufficient.
It is reported in 2005 that the asymmetric epoxidation of several olefins by use of hydrogen peroxide as an oxidizing agent proceeds in a high enantioselectivity manner when a di-μ-oxotitanium salalen complex is used as a catalyst. However, there is a problem in this asymmetric epoxidation that as the di-μ-oxotitanium salalen complex is a giant molecule having a molecular weight of nearly 2000, the synthesis of the complex requires a long time and a high cost. Further, there is also a problem that the method is insufficient in applicability aspect as it goes through intermolecular Meerwein-Ponndorf-Verley reduction for the synthesis of the complex (Non-patent Document 6). Thereafter, it is reported in 2006 that the asymmetric epoxidation of several olefins by use of hydrogen peroxide as an oxidizing agent proceeds in a high enantioselectivity manner when a di-μ-oxotitanium salan complex is used as a catalyst. Although this asymmetric epoxidation overcomes problems in the above-mentioned method by use of di-μ-oxotitanium salalen complex that the synthetic method of complex is difficult and it goes through a special reaction, and thus is an excellent technique, it has problems that optical yield or chemical yield is not sufficient depending on the substrates (Non-patent Document 7 and Patent Document 1).    Patent Document 1: WO 2006/087874 A1    Non-patent Document 1: T. Katsuki, K. B. Sharpless, J. Am. Chem. Soc. (1980), 102, 5974-5796    Non-patent Document 2: E. N. Jacobsen, M. H. Wu, “Comprehensive Asymmetric Catalysis” Ed. by Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H. Springer (1999), Vol. II, 21, pp. 649-677    Non-patent Document 3: T. Katsuki, “Comprehensive Coordination Chemistry II” Ed. by McCleverty, J., Elsevier Science Ltd., Oxford (2003), Vol. 9, Chapter 9.4, pp. 207-264    Non-patent Document 4: L. Shu, Y Shi, Tetrahedron, (2001), 57, 5213-5218    Non-patent Document 5: S. Colonna, H. Molinari, S. Banfi, S. Julia, J. Masana, z, Tetrahedron, (1983), 39, 1635-1641    Non-patent Document 6: K. Matsumoto, Y Sawada, B. Saito, K. Sakai, T. Katasuki, Angew. Chem. Int. Ed. (2005), 44, 4935-4939    Non-patent Document 7: Y Sawada, K. Matsumoto, S. Kondo, H. Watanabe, T. Ozawa, K. Suzuki, B. Saito, K. Sakai, T. Katasuki, Angew. Chem. Int. Ed. (2006), 45, 3478-3480